226 THE PHYSICAL GEOGRAPHY OF THE SEA, 



philosophers off the coast of Florida. This upper current, though 

 colder than its fellow below, is lighter, because it is not so salt. 

 Figure 2 reveals to ns a portion of sea between the parallels of 

 34° and 40° north, exactly in such a physical category as that in 

 which this theory presents the Arctic 'Ocean. Here, along our 

 own shores, the thermal curve loses 12° of heat ; and what does 

 the specific gravity curve gain in the same interval ? Instead of 

 increasing up to 1.027, according to the thermal law, it decreases 

 to 1.023 for the want of salt to sustain it. Now recollect that 

 the great American chain of fresh water lakes never freezes over. 

 Why ? Because (§ 430) of their depth and their vertical circula- 

 tion. The depths below are continually sending water above 32° 

 to the surface, which, before it can be cooled down to the freezing 

 point, sinks again. Now compare the shallow soundings in these 

 lakes with the great depths of the Arctic Ocean ; compute the vast 

 extent of the hydrographic basin which holds this polar sea; gauge 

 the rivers that discharge themselves into it; measure the rain, 

 and hail, and snow that the clouds pour down upon it ; and then 

 contrast its area, and the fresh water drainage into it, with the 

 like of Long Island Sound, Delaware Bay, and the Chesapeake; 

 consider also the volume of diluted sea water between our shore- 

 line and the Gulf Stream ; strike the balance, and then see if the 

 arctic supply of fresh water be not enough to reduce its salts as 

 much as our own fresh water streams are diluting the brine of 

 the sea under our own eyes. The very Gulf Stream water, which 

 the observing vessel left as she crossed the parallel of 34° and en- 

 tered into those light littoral waters, was bound northward. Sup- 

 pose it to have flowed on as a surface current until it, with its salts, 

 was reduced to the temperature of 40°. Its specific gravity at that 

 temperature would have been 1.030, or specifically 30 per cent, 

 heavier than the sea water of our own coasts. Could two such 

 currents of water meet any where at sea, except as upper and 

 under currents ? If water that freezes at 32°, that grows light and 

 remains on the surface as you cool it below 39°, is prevented from 

 freezing in our great fresh water lakes by vertical circulation, 

 how much more would both vertical and horizontal circulation 

 prevent congelation in the open polar sea, that is many times 

 deeper and larger than the lakes, and the water of which con- 

 tracts all the way down to its freezing point of 27°.2. 



